1. Field of the Invention
This invention relates specifically to air bearing sliders for use in a magnetic recording drive. In particular, it relates to a method and apparatus for providing stronger and more broadly distributed negative pressure by the use of dual cross bars. This invention provides more stable static and dynamic flying attitude with a compensating slider size reduction and a wide variation of skew angle.
2. Description of the Related Art
Magnetic recording systems transfer data through transducers that are supported by an air bearing film or layer as they move relative to the surface of a magnetic recording disk. Such transducers need to either xe2x80x9cflyxe2x80x9d at just a few micro-inches above a rotating disk surface (flying-type heads), or contact the rotating disk slightly within a safe range (pseudo contact-type heads). The air bearing film is produced by the pressurization of air as it flows between the rotating disk surface and the magnetic head assembly (also called the slider body).
These assemblies provide a non-contact transducing mechanism between a magnetic transducer and a fast rotating recording medium. However, to obtain the best data transfer performance without causing serious tribological problems, this requires that a stable, constant spacing be maintained between a flying transducer (on the slider body) and the magnetic recording disk.
In order to achieve the high-speed data access rate and smaller drive size requirements, rotary actuators have become the norm, as opposed to linear actuators. With the use of rotary actuator, the airflow under the slider is no longer substantially unidirectional, but varies widely in angle with respect to the longitudinal axis of the slider.
As the nominal flying height (the distance between the slider body and the rotating disk surface) of the flying slider decreases, the magnetic transducer achieves a higher resolution between individual data bit locations on the disk. Thus, a close space between the flying slider and the rotating disk, coupled with a very narrow transducer gap and a very thin magnetic recording film, allows for a higher recording capacity with very short wavelength and high frequency features. A constant spacing between the flying head slider body and the disk also minimizes the fluctuations in signal amplitude, thereby optimizing signal resolution. Finally, a constant low flying height over whole data area is the essential factor for an optimized higher density recording process regardless of skew angle variation and increasing rotating disk speed.
Therefore, to achieve a higher recording density the flying height must be reduced as much as possible without causing reliability problems. Problems can occur, however, when excessive and unwanted variations in the flying height result in contact between the flying slider and the rapidly rotating recording medium. Any such contact leads to wear of the slider and the recording surface, and in certain conditions, can be catastrophic to the operation of the disk drive.
Accordingly, development efforts continue to strive for lower and lower flying heights while trying to provide uniform or optimum flying height conditions across a range of flying conditions. Some tactics that are used are tangential velocity variations from the inside to the outside tracks and high speed track seeking movement.
Another way to achieve a high-speed access rate for stored data and to obtain a smaller drive size, is through the use of a rotary actuator rather than a linear actuator. By using a rotary actuator, the airflow under the slider is no longer substantially unidirectional, but varies widely in angle with respect to the longitudinal axis of the slider. The angle of the airflow with respect to the longitudinal axis of the slider is called the skew angle. In accessing the magnetic disks for recording, and playing back from disks using a rotary type actuator, the magnetic transducer continuously experiences air velocity and skew angle variations while moving from one data track to another data track of the disk in response to commands from a voice coil motor (VCM) controller. Large amount of skew angle and fast accessing movement of rotary actuator can cause a severe reduction of flying height, especially at inner and outer tracks.
Disk circumferential speed increases linearly from the inner diameter (ID) to the outer diameter (OD) of the rotating disk. Because a slider typically flies higher as the velocity of the disk recording medium increases, there is a tendency for the slider""s outer rail to fly higher than the inner rail. Therefore, the flying slider has a structure that ensures that a roll angle can be generated in an attempt to counteract the tendency of the outer rail to fly higher than the inner rail. The roll angle is defined as the tilt angle between the principal plane of the slider in the radial direction of the disk and the principal plane of the disk surface.
The ability to control or generate changes in the roll angle are important to counteract other forces generated during disk drive manufacture or operations. Some of these forces or factors that must be compensated for include: manufacturing errors in the gimbals which attach the slider to the suspension arm; dynamic forces applied to the air bearing slider by the track accessing arm during tracking accessing; and varying skew angles tangential to the disk rotation as measured from the slider center line.
For example, regardless of the particular skew angle with respect to the direction of air flow, unequal pressure distribution develops between the outer and inner side rails. This causes the slider to fly with the inner rail much closer to the disk surface than the outer rail. As a result, the probability of physical contact with the disk surface at this slider""s minimum flying height increases. Therefore, there is a continuing effort to develop air bearing sliders that carry a transducer as close to the disk surface as possible with a constant flying height and roll angle regardless of the varying flying conditions such as disk velocity and skew angle variation.
Air bearing sliders used in disk drives also typically have a leading edge (a front portion) and a trailing edge (a rear portion). Generally, the sliders have tapered or shallowly-etched portions at the leading edge to lift up slider by squeezing incoming air, and longitudinal air bearing rails that extend from the leading edge all or part way to the trailing edge. Airflow is developed in the direction on the disk surface and applied to cause the flying head slider to float off the rotating disk surface against the resiliency of the suspensions. Pitch angle is introduced through the fact that the flying height of the leading edge is generally different from that of the trailing edge. The pitch angle is defined as the tilt angle between the principal plane of the slider body in the tangential direction of the rotating disk and the principal plane of the disk surface.
The pitch angle is positive in the normal case in which the flying height of the trailing edge of the slider is lower than that of the leading edge of the slider. This is the preferred state for stable head flying. When the leading edge flying height is lower than the trailing edge flying height, however, the slider has a negative pitch angle, which can cause unstable head flying. In particular, with such a negative pitch angle, the possibility exists that there could be sudden physical contact between flying head and rotating medium.
Furthermore, if the designed positive pitch angle is too small, the possibility exists that the slider will dip down or inadvertently transition to a negative pitch angle orientation, caused by internal or external interference, for example, and the leading edge of the slider may hit the rotating disk. On the other hand, if the designed pitch angle is too large, the air stiffness needed for stable flying can be disadvantageously reduced, which may also result in a collision with the disk. Therefore, to maintain stability while avoiding the negative pitch angle situation, the slider should be configured such that the pitch angle can be controlled to fall within an optimum range.
Another factor to consider regarding pitch angle is the general tendency for the pitch angle to increase when the skew angle increases as the slider is positioned nearer to the outer diameter of the disk. Thus the pitch angle should fall within a safe range regardless of the skew angle variations to ensure the desired dynamic performance reliability of the head/disk interface.
A small pressure difference is generated beneath inner and outer side rails of the flying slider even with a zero skew angle condition, because of a small difference in the linear velocity of the disk at the two different locations beneath the two rails. Thus, even without skew, this pressure difference between two side-rails makes the slider roll slightly. Also, the skew-angle of the airflow further causes the slider to roll even more, such that the flying height is not uniform under all of the rails.
In a disk drive, a positive roll occurs when the inner rail rolls away from the disk surface, while a negative roll occurs when the inner rail rolls toward the disk surface. When roll lowers a corner of the slider, the possibility is increased that the head will come into contact with the disk surface. Also, a roll that raises one corner of the slider can increase the distance of the read and write heads from the disk surface, making data errors in the same manner that increasing the fly height of the slider causes data errors. Finally, the variation in roll angle as a function of actuator skew needs to be substantially reduced or eliminated to achieve a stable flying attitude and a reliable data transfer between head and media. Transducers are generally located at the trailing edge of the center rail, and a bigger roll angle can make for a much lower minimum flying height point, which is bad for head-disk interface reliability. This can be seen in FIGS. 1A and 1B, which are rear views of a head and transducer, showing different roll angles.
As shown in FIGS. 1A and 1B, a head 1 and transducer 3 are provided for reading information from a disk 7. FIG. 1A shows a rear view of the head 1 and transducer 3 when they experience a small roll angle. FIG. 1B shows a rear view of the head 1 and transducer 3 when they experience a large roll angle. In each case, the head 1 and transducer 3 have a minimum flying height that indicates how close the head 1 and transducer 3 get to the surface of the disk 7.
When there is a small roll angle xcex8A, as shown in FIG. 1A, the head 1 and transducer 3 maintain a minimum flying height of A. However, where there is a large roll angle xcex8B, as shown in FIG. 1B, the head 1 and transducer 3 maintain a minimum flying height of B. If the transducer 3 in both FIGS. 1A and 1B has the same transducer flying height, the minimum flying height A will be larger than the minimum flying height B, as a function of the difference in their roll angles.
During the high-speed rotation of a hard disk associated with the flying head slider, a suitable airflow is produced through an air viscosity effect and is applied to support the flying head slider. The flying head slider moves from an innermost disk region to an outermost disk region with a rotary actuator. As the skew angle of the flying head slider progressively changes, and the direction of the airflow progressively increases, a negative pressure is developed in the control grooves in proportion to the linear velocity. Consequently, the flying head slider remains floating off the disk surface safely by a small distance over the full disk surface range. Different slider geometry types have different gas bearing characteristics.
FIG. 2 is a schematic perspective view of a conventional a negative pressure air bearing (NPAB) type tri-pad slider. This conventional slider 10 includes a slim hexahedron body 5, first and second air-bearing surfaces 11 and 12, first and second tapered or sloped portions 13 and 14, a cross bar (or cross rail) 15, a forward cavity 16, a negative, or sub-ambient, pressure cavity 17, and a central island 19. A transducer 20 is preferably mounted at the rear portion of the central island 19, with reference to the disk rotation.
The first and second air-bearing surfaces 11 and 12 are formed in parallel at a predetermined height on the surface of the slim hexahedron body 5 extending lengthwise from a leading edge portion, or front, of the slider 10 to a trailing edge portion, or rear, of the slider 10, with respect to the direction of disk rotation. The first and second sloped portions 13 and 14 are respectively formed at each leading edge portion of the first and second air-bearing surfaces 11 and 12. The cross bar 15 has the same height as the first and second air-bearing surfaces 11 and 12, and is formed between the first and second air-bearing surfaces 11 and 12 near the leading edge between the air-bearing surfaces 11 and 12 proximate to the sloped portions 13 and 14. The forward cavity 16 is formed by the cross bar 15, the first and second air-bearing surfaces 11 and 12, and the first and second sloped portions 13 and 14, and faces the forward portion of the slider 10. The negative pressure cavity 17 is formed by the cross bar 15 and the first and second air-bearing surfaces 11 and 12, and faces the rear portion of the slider 10. The central island 19 has the same height as the first and second air-bearing surfaces 11 and 12, and is formed between the negative pressure cavity 17 and the trailing edge of the slider 10.
In this conventional design, air within a very thin boundary layer rotates together with the rotation of the disk due to surface friction. The disk drags air under the slider 10 and along the air bearing surfaces in a direction approximately parallel to the tangential velocity of the disk. When passing between the rotating disk and the slider 10, the air is compressed by the sloped portions 13 and 14 on the leading edge of the air-bearing surfaces 11 and 12. In a similar manner, passing air is also compressed by the central island 19. This pressure creates a hydrodynamic lifting force at the ramp section which is sustained along each of the air-bearing surfaces 11 and 12, and a hydrodynamic lifting force at the central island 19. This results in a lifting force that allows the slider 10 to fly over the disk surface. In this way, the air-bearing surfaces 11 and 12, and the central island 19 function as pneumatic bearings, and thus form a positive pressure region for the slider 10 at a portion along an axis of an air flow generated by a rotation of the magnetic disk.
The cross bar 15, in conjunction with the air-bearing surfaces 11 and 12, creates the negative pressure cavity 17 in proximity to the central surface portion of the body 5 and downstream of the cross bar 15. Since the pressure of the air passing over the cross bar 15 is diffused as it passes the negative pressure cavity 17, a pulling or suction force is downwardly applied on the slider which reduces the suspension gram load, or suspension force, i.e., the downward force applied by the suspension of the slider 10, and provides the advantage of a fast take off from the disk surface.
The operation of forces on the slider 10 both with and without a negative pressure cavity is shown in FIGS. 3A and 3B. FIG. 3A shows the case without a negative pressure cavity and FIG. 3B shows the case with a negative pressure cavity. In each instance, for a slider 10 to maintain a substantially constant height over a disk 7, the upward and downward forces must be equal.
As shown in FIG. 3A, when the slider does not have a negative pressure cavity, the downward pressure comes from a first suspension gram load, or first suspension force X, and the upward pressure comes from an air bearing surface (ABS) supporting force Y, caused by the hydrodynamic lifting force created by air-bearing surfaces.
As shown in FIG. 3B, when the slider does have a negative pressure cavity, the downward pressure comes from both a second suspension force Xxe2x80x2 and a negative pressure force Z created by the suction caused by the negative pressure cavity. The upward pressure continues to come from the ABS supporting force Y, as in FIG. 3A.
If the ABS supporting force Y remains the same in the sliders 10 in FIGS. 3A and 3B, then the first suspension force X must equal the sum of the second suspension force Xxe2x80x2 plus the negative pressure force Z. As a result, the suspension force, or suspension gram load, can be reduced through the use of a negative pressure cavity.
The counter action between the positive and negative forces caused by the air-bearing surfaces 11 and 12, the central island 19, and the negative pressure cavity 17 also reduces the sensitivity of the slider flying height relative to disk velocity and increases the slider stiffness characteristics. This suspension load reduction can bring significant improvement for conventional contact start stop (CSS) performance.
However, the NPAB tri-rail slider of FIG. 2 does suffer some drawbacks. For example, the amount of negative pressure in the a negative pressure cavity 17 is dependent upon the air flow direction, meaning that differing pressures will exist at differing skew angles. This results in a non-uniform operation along the full diameter of the disk. In particular, higher skew angles may cause more severe negative roll fluctuations compared to conventional tapered tri-rail flat slider. Also, there is a tendency for debris to gather at the cross-rail 15 in the forward cavity 16. Such debris can ultimately have an adverse effect on performance since the accumulated particles may cause head crashes and undue wear of the head and disk.
In order to achieve more the stable and lower flying height required to get higher density recording without causing several tribological problems, the slider size itself needs to be smaller. In order to obtain a faster data transfer rate, the disk rotation speed needs to be faster and the movement of flying head itself needs to be sped up, while retaining a constant data handling reliability. To simultaneously satisfy these requirements, the air bearing shape of flying slider needs to be continuously improved.
In this invention, a novel slider design with a more enforced and well-distributed negative pressure around central cavity sections is introduced as a suitable candidate for the purpose of achieving a higher density and better performance. Statically and dynamically stable flying attitude with smaller slider size and lower flying height has been successfully obtained through this invention.
An object of this invention is to provide a negative pressure air bearing slider that experiences minimal changes in flying height and pitch angle and roll angle over a broad range of velocity and skew angle variations in a disk drive system.
Another object of the invention is to provide a negative pressure air bearing slider that experiences constant and stable air bearing stiffness with large skew angle variations in a disk drive system.
Another object of the invention is to provide a negative pressure air bearing slider that shows minimized particle accumulation on the whole air bearing surface without sections showing drastic air flow change.
A further object is to provide a negative pressure air bearing slider that exhibits smaller sensitivity to external disturbances and environmental changes with a well-balanced force and momentum equilibrium condition for a flying slider.
In accordance with these objects of the invention, a pseudo contact negative pressure air bearing (NPAB) slider is provided, including a slider body for flying above a surface of a recording disk during relative rotation of the recording disk, the slider body having a principal surface for confronting the disk surface, the principal surface having a lead portion, a rear portion, a first side portion and a second side portion, wherein the lead portion is spaced upstream of the rear portion relative to a longitudinal direction of the slider body which is coincident with a tangential rotational direction of the recording disk, and wherein the first side portion is spaced from the second side portion relative to a lateral direction of the slider body.
The NPAB slider also includes first and second projections extending from the lead portion of the principal surface of the slider to a midpoint of the slider, the first and second projections being spaced apart from each other in the lateral direction of the slider body, a first cross bar formed between the first and second projections, third and fourth projections extending from the midpoint of the principal surface of the slider to the rear portion of the slider, the third and fourth projections being spaced apart from each other in the lateral direction of the slider body, and a second cross bar formed between the third and the fourth projections.
The NPAB slider also includes a central island formed between the second cross bar, the third and fourth projections, and the rear portion of the slider. A transducer is mounted on the central island so as to be suspended over the disk surface while the disk is rotating.
The first cross bar and the first and second projections define a first negative pressure air cavity for the slider body, and the second cross bar and the third and fourth projections define a second negative pressure air cavity for the slider body.
The NPAB slider may also comprise first and second slanted walls, the first slanted wall being formed between the second cross bar and the third projection, and the second slanted wall being formed between the second cross bar and the fourth projection. The second cross bar, the first and second slanted walls, and the third and fourth projections define a second negative pressure air cavity for the slider body. The second cross bar and the first and second slanted walls preferably form a convex shape, with respect to the lead portion of the slider.
The NPAB slider may also comprise a central shallowly-etched step formed proximate to the lead portion of the slider, the central shallowly-etched step having a height less than that of the first and second projections.
The transducer on the NPAB slider is preferably mounted on the central island proximate to the rear portion.
The first cross bar may have a first air channel formed in it to allow air to flow from the lead portion of the slider to the first negative pressure air cavity. Similarly, the second cross bar may have a second air channel formed in it to allow air to flow from the first negative pressure air cavity to the second negative pressure air cavity.
The first and third projections preferably define a third air channel from the first negative pressure air cavity to the first side portion, and the second and fourth projections preferably define a fourth air channel from the first negative pressure air cavity to the second side portion.
The first cross bar may be shallowly etched to regulate the flow of air from the lead portion to the first negative pressure air cavity. Likewise, the second cross bar may be shallowly etched to regulate the flow of air from the first negative pressure air cavity to the second negative pressure air cavity.
Also in accordance with the objects of this invention, a negative pressure air bearing (NPAB) slider, is provided, including a slider body for flying above a surface of a recording disk during relative rotation of the recording disk, the slider body having a principal surface for confronting the disk surface, the principal surface having a lead portion, a rear portion, a first side portion and a second side portion, wherein the lead portion is spaced upstream of the rear portion relative to a longitudinal direction of the slider body which is coincident with a tangential rotational direction of the recording disk, and wherein the first side portion is spaced from the second side portion relative to a lateral direction of the slider body.
The NPAB slider also includes first and second primary projections extending from the lead portion of the principal surface of the slider to the rear portion of the slider, the first and second primary projections being spaced apart from each other in the lateral direction of the slider body, the first and second primary projections each including a front section proximate to the lead portion, a rear section proximate to the rear portion, and a middle section between the front and rear sections, the middle section being more narrow than either of the front or rear sections, and a primary cross bar placed between the front sections of the first and second primary projections.
The NPAB slider also includes first and second secondary projections, being smaller in length than the first and second primary projections, being spaced apart from each other in the lateral direction of the slider body, and being placed proximate to the middle sections of the first and second primary projections, and a secondary cross bar placed between the first and second secondary projections, in the direction facing the lead portion.
The NPAB slider also includes a central island formed between the secondary cross bar, the first and second primary projections, and the rear portion of the slider. A transducer is mounted on the central island, so as to be suspended over the disk surface while the disk is rotating.
The primary cross bar and the first and second primary projections define a primary negative pressure air cavity for the slider body, while the secondary cross bar and the first and second secondary projections define a secondary negative pressure air cavity for the slider body. The secondary cross bar is preferably convex with respect to the lead portion of the slider.
The NPAB slider may also comprise a central shallowly-etched step, having a height less than that of the first and second projections, formed proximate to the lead portion of the slider.
The transducer is preferably mounted on the rear section of the central island.
The primary cross bar preferably has a primary air channel formed in it to allow air to flow from the lead portion of the slider to the primary negative pressure air cavity. Similarly, the secondary cross bar has a secondary air channel formed in it to allow air to flow from the primary negative pressure air cavity to the secondary negative pressure air cavity.
The first primary projection and the first secondary projection preferably define a first air channel from the primary negative pressure air cavity to the rear portion, while the second primary projection and the second secondary projection preferably define a second air channel from the first negative pressure air cavity to the rear portion.
The primary cross bar can be shallowly etched to regulate the flow of air from the lead portion to the primary negative pressure air cavity. Likewise, the secondary cross bar may be shallowly etched to regulate the flow of air from the primary negative pressure air cavity to the secondary negative pressure air cavity.
In accordance with the objects of this invention, a negative pressure air bearing slider is also provided that includes a slider body, for flying above a surface of a recording disk during relative rotation of the recording disk, the slider body having a lead portion and a rear portion, first and second projections formed on the slider body, the first and second projections being spaced apart from each other in a lateral direction of the slider body, and providing a plurality of positive forces to support the slider over the disk, a cross bar formed between the first and second projections, a first negative pressure air cavity proximate to the lead portion for providing a first negative force, pulling down the slider towards the disk, a second negative pressure air cavity proximate to the rear portion for providing a second negative force, pulling down the slider towards the disk, a central island formed between the cross bar, the first and second projections, and the rear portion of the slider, and providing an additional positive force, and a transducer mounted on the central island, so as to be suspended over the disk surface while the disk is rotating.
The plurality of positive forces, the additional a positive force, and the first and second negative forces are preferably balanced around the center of mass of the slider to keep the slider at a constant height over the disk.